they seem to be at war with all mankind..

Those Sikhs who adhere to the original doctrines of Nanac are called Khalasa; they are less fanatical and warlike then the Singhs or followers of Guru Govind. Of these latter, a peculiar
class is called Acalis, or immortals, and sometimes Nihungs. Their fanaticism, Bumes observes, borders on insanity, and they seem to be at war with all mankind.. .They are a lawless and sanguinary class, and would have rendered the country desolate, had they not been vigorously coerced by Runjeet Singh.
Edward Thornton, A gazetteer of the Countries adjacent to India on the north-west: includingSinde, Afghanistan, the Punjab and the neighbouring states, 1844.

Bhai Mani Singh Shaheed Nihang Singh

Many people see Bhai Mani Singh as a scholar, and martyr, the earliest accounts of his life also narrate that he was a Nihang Singh, as were his sons. Kavi Seva Singh in 1800 AD records:

ਸੇਵਾ ਕਰੇ ਆਲਸ ਕੋ ਤਿਆਗੈ।

[Bhai Mani Singh] Doing Seva he renounced lazyness.

ਸੇਵਾ ਪਹਿਰ ਨਿਸ ਰਹਿੰਦੀ ਜਾਗੈ।

Everyday he would wake up at a quarter watch.

ਕਰ ਇਸ਼ਨਾਨ ਜਪੈ ਜਪੁ ਜਾਪੁ ।

Waking up he would bath and read Jap and Jaap sahib [Nitnem]

ਗੁਰਬਾਣੀ ਕਾ ਬਢ ਪ੍ਰਤਾਪ।

He shone greatly with the light of Gurbani.

ਸਾਜ ਦੁਮਾਲਾ ਸ਼ਸਤ੍ਰ ਪਹਿਰੈ।

He would tie a Dumalla [High Turban] and wear Weapons.

ਨੀਲੰਬਰ ਗਜ ਸਵਾ ਕਛਹਿਰੈ।

Wearing blue and a Sava Gajh Kechera [A Nihang tradition].

ਪਕੜ ਦੁਤਾਰਾ ਗਾਵੈ ਬਾਣੀ ।

Holding onto the Double-edged sword he would sing Bani.

ਆਸਾ ਵਾਰ ਸੁਖਾਂ ਦੀ ਖਾਣੀ।

Asa di Var the treasure of happyness.

ਤੀਜੇ ਪਹਿਰ ਸ਼ਹੀਦੀ ਦੇਗ।

At the third watch he would take Shaheedi Degh [Parshad of Martyrs]

ਜਗ ਮੇਂ ਚਲੇ ਦੇਗ ਔ ਤੇਗ।

In this world the Guru gave the order of the Degh and Tegh.

ਸੇਵਾ ਹਰੀ ਸਿੰਘ ਕੀ ਕਰਨੀ।

He would serve the good Singhs.

ਏਕ ਜਿਹਵਾ ਸੇ ਜਾਇ ਨ ਬਰਨੀ।੧੮੫।

With one tongue his life-style cannot be said.

The son of Bhai Mani Singh clearly a Nihang Singh and a Shahid Singh, his fresco is present at Gurdwara Baba Atal Rai, Sri Darbar sahib complex, Sri Amritsar.

Shaan of Sant Baba Isher Singh ji

Why are you so engrossed in worries? Why are you afraid of some one? Who may kill you? The soul is immortal; it neither dies nor takes birth. The present is here and now, the past is irrecoverable and the future will be good. Don't fret over the past and don't be worried about the future. The present is going on. Why do you cry? What did you lose? When you were born, what did you bring along, which has been lost? What did you produce which has been perished? It is here that you gained and it is here that you lose. The man comes to; and goes from world, empty handed. What you own today was not yours yesterday and will not be yours tomorrow. It does not and will not belong to anyone. You consider it your own and rejoice. This happiness of possession leads you to utter grief. Yours is this world. Start from where you feel to; stay where you desire and wind up where you want to. It has no beginning and no end. You don't fear anyone, but yourself. You are the fright and also the frightened. Change is the truth of life. What you consider as death is life in reality. In a moment a multi-millionaire is turned pauper. Give up the feeling of possession, great & the mean; differentiation of friend & foe. Then all is yours and you for everyone. Your corporeal being is a product of air, water and fire and it merges into the same leaving behind neither blood nor bones. Still yours existence remains the same. Then ponder over what you are. Wake up! and become the eternal sons of the Almighty. You are the great and unique manifestation of Nature's power. All the divine powers are possessed by you, like a tree hidden in the seed. In fact you don't fear anybody; you don't have any worry, suspicion, pain or grief. You are His dear ones. Surrender yourself completely to Him. Always, remember the "Waheguru" (God) to achieve salvation. Let your life be guided by the saying "Whatever God wills, is good". Be content with the will of God. Remember Him both in pleasure & pain.

Shaan - Sant Baba Isher Singh Ji (Rara Sahib)

Mira Bhai - Hari tum haro - There is no sorrow when I am joined to You

Hari tum haro jan ki pir
Hari, please remove the suffering of the people
Draupadi ki laj rakhyo tum badhyo cir
You preserved Draupadi's honor by increasing the
length of the garment that covered her.
bhakat karan roop narahari dharyo ap sharir
For the sake of your devotee, you took on the form of Nrsimhadeva
Harinakashyapa mara leenho dharyo nahina dhir
To kill the demon Hiranyakashyap,
you took on the form of a beast.
bhoodathe gaja raja rakhyO liyo bahar neer
You dragged the elephant king out of the water and saved him from the crocodile's jaws.
dasa meera lal giridhar dukh jahan tahan pir
Your servant (dAsa) Meera (the saint and composer) is always with you and finds no sorrow when I'm with you.

Guru Nanak in Rag Maru, Adi Guru Granth sahib p. 1038 states - “From the Primal Lord, came the Ten Avtars (who constitute Narsingh Avtar, Bavan Avtar, Rama Avtar, Krishna Avtar and others)” At p. 1156, Rag Bhairo, Gru Arjan Dev stated - “He created millons of incarnations (Avtars) of Vishnu.” At p. 1279, in Rag Malar, Guru Nanak stated - “The Ten Incarnations, Rama, the King came into being. According to His Will, Rama quickly killed all the demons.”

Shastar Vidiya

'We have seen that one great distinguishing feature of their system is that war is made an essential part of religion. To indicate their belief in this doctrine, they worship the military weapons of their Gurus.'
('Religious Thought And Life In India', By Monier Williams (1883), Part 1, Pa. 172)

Good over evil

ਪਉੜੀ ॥ ਹਰਿ ਕੀ ਭਗਤਾ ਪਰਤੀਤਿ ਹਰਿ ਸਭ ਕਿਛੁ ਜਾਣਦਾ ॥ ਹਰਿ ਜੇਵਡੁ ਨਾਹੀ ਕੋਈ ਜਾਣੁ ਹਰਿ ਧਰਮੁ ਬੀਚਾਰਦਾ ॥ ਕਾੜਾ ਅੰਦੇਸਾ ਕਿਉ ਕੀਜੈ ਜਾ ਨਾਹੀ ਅਧਰਮਿ ਮਾਰਦਾ ॥ ਸਚਾ ਸਾਹਿਬੁ ਸਚੁ ਨਿਆਉ ਪਾਪੀ ਨਰੁ ਹਾਰਦਾ ॥ ਸਾਲਾਹਿਹੁ ਭਗਤਹੁ ਕਰ ਜੋੜਿ ਹਰਿ ਭਗਤ ਜਨ ਤਾਰਦਾ ॥੧੮॥
har kee bhagathaa paratheeth har sabh kishh jaanadhaa. The Lord's devotees have faith in Him. The Lord knows everything. har jaevadd naahee koee jaan har dhharam beechaaradhaa. No one is as great a Knower as the Lord; the Lord administers righteous justice. kaarraa a(n)dhaesaa kio keejai jaa naahee adhharam maaradhaa Why should we feel any burning anxiety, since the Lord does not punish without just cause? sachaa saahib sach niaao paapee nar haaradhaa. True is the Master, and True is His Justice; only the sinners are defeated. saalaahihu bhagathahu kar jorr har bhagath jan thaaradhaa 18. O devotees, praise the Lord with your palms pressed together; the Lord saves His humble devotees. 18

A blind Nihang Singh does beautiful Kirtan at the Gurdwara of Mata Sahib Deva ji

ਸੋਰਠਿ ਮਹਲਾ ੫ ॥ ਗੁਰ ਕਾ ਸਬਦੁ ਰਖਵਾਰੇ ॥ ਚਉਕੀ ਚਉਗਿਰਦ ਹਮਾਰੇ ॥ ਰਾਮ ਨਾਮਿ ਮਨੁ ਲਾਗਾ ॥ ਜਮੁ ਲਜਾਇ ਕਰਿ ਭਾਗਾ ॥੧॥ ਪ੍ਰਭ ਜੀ ਤੂ ਮੇਰੋ ਸੁਖਦਾਤਾ ॥ ਬੰਧਨ ਕਾਟਿ ਕਰੇ ਮਨੁ ਨਿਰਮਲੁ ਪੂਰਨ ਪੁਰਖੁ ਬਿਧਾਤਾ ॥ ਰਹਾਉ ॥ ਨਾਨਕ ਪ੍ਰਭੁ ਅਬਿਨਾਸੀ ॥ ਤਾ ਕੀ ਸੇਵ ਨ ਬਿਰਥੀ ਜਾਸੀ ॥ ਅਨਦ ਕਰਹਿ ਤੇਰੇ ਦਾਸਾ ॥ ਜਪਿ ਪੂਰਨ ਹੋਈ ਆਸਾ ॥੨॥੪॥੬੮॥

Sorat'h, Fifth Mehla:
gur kaa sabadh rakhavaarae
The Word of the Guru's Shabad is my Saving Grace.
choukee chougiradh hamaarae
It is a guardian posted on all four sides around me.
raam naam man laagaa
My mind is attached to the Lord's Name.
jam lajaae kar bhaagaa 1

The Messenger of Death has run away in shame. 1
prabh jee thoo maero sukhadhaathaa
O Dear Lord, You are my Giver of peace.
ba(n)dhhan kaatt karae man niramal pooran purakh bidhhaathaa rehaao
The Perfect Lord, the Architect of Destiny, has shattered my bonds, and made my mind immaculately pure. Pause
naanak prabh abinaasee
O Nanak, God is eternal and imperishable.
thaa kee saev n birathhee jaasee
Service to Him shall never go unrewarded.
anadh karehi thaerae dhaasaa
Your slaves are in bliss;
jap pooran hoee aasaa 2468
chanting and meditating, their desires are fulfilled. 2468

Anglo Sikh war, a Nihang Singh, and Dasam Granth

Colonel Hodson records in the Anglo-Sikh wars that:

One fine old Nihang beat off four sowars, one after another and kept them at bay. I then went at him myself. He instantly rushed to meet me like a tiger, yelling wah guruji, and accompanying each shout with a terrible blow of his talwar. I guarded the first three or four first, but he pressed so close to my horse’s reins that I could not get a fair cut in return. At length I pressed in my turn upon him so sharply that he missed his blow and I caught his talwar back-handed with my bridle-hand, wrenched it from him and cut him down with the right, having received no further injury than a severe cut across the fingers. I never beheld such deperation and fury in my life. It was not human scarcely.

Guru Gobind Singh writes at the end of Krishnaavtar in the Sri Dasam Granth that:

Blessed is the life of that person in the world who recites the Holy Name with his mouth and contemplates war against evil in his heart. Who regards the body as a temporary vesture and uses the boat of the Lord's Name to cross the rough world-ocean. Who makes a closet of patience in his body and illumines the mind with the lamp of divine knowledge, Who takes up the broom of (spiritual) wisdom in his hands and sweeps away all cowardice and falsehood.